In conventional prior art receiver circuit design, receiving multiple signals simultaneously of possible different wireless standards requires multiple complete receiver circuits. Consider a first example prior art receiver capable of simultaneous multiple signal reception as shown in FIG. 1. The receiver, generally referenced 10, comprises two separate RX circuits each comprising antenna 12, analog front-end RX circuit 14 (analog RX1 and analog RX2), local oscillator 16 (LO1 and LO2), analog to digital converter 18 (ADC1 and ADC2), digital back-end RX circuit 20 (digital RX1 and digital RX2) and digital baseband circuit 22 (DBB1 and DBB2).
A diagram illustrating the frequency spectrum of two received RF signals and their corresponding local oscillator clock signals generated by the receiver is shown in FIG. 2. The RF1 signal 29 having center frequency fc1 is mixed with local oscillator signal fLO1 28. Similarly, the RF2 signal 26 having center frequency fc2 is mixed with local oscillator signal fLO2 24.
In operation, the first RX circuit receives an input signal RF1 and outputs a DATA_OUT1 signal. The local oscillator signal fLO1 is used by analog RX1 circuit to downconvert the RF1 signal to an IF, of center frequency fc1-fLO1, or baseband signal. The second RX circuit receives an input signal RF2 and outputs a DATA_OUT2 signal. The local oscillator signal fLO2 is used by analog RX2 circuit to downconvert the RF2 signal to an IF, of center frequency fc2-fLO2, or baseband signal. Thus, not only are separate LO circuits required in the circuit but separate complete receive paths are needed to process both RF signals.
A diagram illustrating the frequency spectrum of both RF signals after downconverting using respective local oscillator signals is shown in FIG. 3. The first RX circuit downconverts the RF1 signal 30 and then filters it using low pass filtering (LPF) 32. Similarly, the second RX circuit downconverts the RF2 signal 34 and then filters it using low pass filtering (LPF) 36.
The local oscillator (i.e. frequency synthesizer) design for RF applications, however, requires significant chip area and is very power intensive, especially in deep-submicron processes, due to the requirement of a high-Q inductor. Thus, eliminating a single inductor and associated synthesizer circuitry can potentially free up as much as 300K gates for other digital tasks, depending on the process technology used.
A block diagram illustrating a second example prior art transceiver incorporating separate receive and transmit local oscillators is shown in FIG. 4. The transceiver, generally referenced 40, comprises a duplexer 43 coupled to antenna 42, RX circuit 44 for receiving RF1 and generating DATA_OUT1, local oscillator (LO1) 45 generating fLO1, TX circuit 46 for receiving DATA_IN2 and generating RF2 and local oscillator (LO2) 47. The transmitter may comprise a polar transmitter with phase/frequency modulation 48 applied to the local oscillator signal fLO2. Note that two separate local oscillators 45 and 47 are used for both transmit and receiver circuits.
Normally, full-duplex wireless standards, such as WCDMA require simultaneous transmit and receive operations using a transceiver such as that shown in FIG. 4. To accommodate simultaneous transmission and reception, a frequency band separation is inserted between the transmit and receive frequency bands. This, however, requires two local oscillators which must be isolated in order to avoid any frequency pulling between each other. This is the case for wireless standards such as 3G and 4G, including LTE, WiMAX, WCDMA and other standards that utilize frequency division duplex (FDD) whereby the transmitter and receiver must operate at the same time.
As in the case of multiple simultaneous signal reception in the circuit of FIG. 1, the local oscillator circuit requires significant chip area and power consumption due to the need for a high-Q inductor. Therefore, eliminating the inductor and associated synthesizer circuitry can free up significant chip area and reduce power consumption.
There is thus a need for a receiver capable of simultaneous multiple signal reception that does not require the use of separate individual local oscillators for the reception of each RF signal. In addition, there is a need for a transceiver capable of simultaneous transmission and reception that does not require the use of separate individual local oscillators for transmitter and reception operation. There is a further need for a receiver capable of simultaneous multiple signal reception that does not require the use of separate individual receive paths.